The present invention relates to a flexible tube for an endoscope.
A flexible tube for an endoscope is generally formed as follows.
1. Belt-like material made of metal or synthetic resin is wound in a spiral fashion at a predetermined diameter to form a spirally-wound tube.
2. Thus formed spirally-wound tube is covered with a braided wire tube which is formed by braiding thin wires.
3. Further, the braided wire tube is coated, on its outer surface, with a sheath made of synthetic resin.
Recently, the sheath is formed in accordance with an extrusion coating method. However, when the sheath is applied on the outer surface of the braided wire tube in accordance with the extrusion coating method, the innermost tube, i.e., the spirally-wound tube, can move freely with respect to the sheath, which makes the flexible tube too flexible, and buckling phenomenon may occur, due to the shift of the spirally-wound tube, when such a flexible tube is used.
In order to avoid such a problem, conventionally, when the extrusion coating is done, the melted resin (i.e., the melted sheath material) is put into the interstices of the braided wire tube such that the sheath material (i.e., the synthetic resin) is filled densely in clearances between windings, along a pitch (axial) direction, of the spirally-wound tube. An example of such a structure is described in Japanese Patent Publication No. HEI2-51601.
If the sheath material is filled densely at the clearance of each winding of the spirally-wound tube and then the sheath material is hardened, the movement of the spirally-wound tube is restricted, and accordingly, the flexibility of the flexible tube is significantly deteriorated.
In the meantime, if the endoscope is to be deeply inserted in the human cavity, it is preferable that the flexible tube bends easily only in a desired direction and hardly bends in undesired directions.
However, in the conventional endoscope, the flexibility of the flexible insertion tube is the same in any direction. Therefore, if the flexible tube is formed to bend easily, it may bend both in desired and undesired directions, while if the flexible tube is formed not to bend easily in the undesired directions, the tube is also prevented from bending easily in the desired direction.
It is therefore an object of the present invention to provide an improved flexible tube for an endoscope, which is formed by providing a sheath on a braided tube covering the spirally-wound tube, and still has an excellent flexibility.
Another object of the present invention is to provide an improved flexible tube for an endoscope which has directivity in bending direction.
For the above object, according to a first aspect of the present invention, there is provided a flexible tube for an endoscope, provided with: a spirally-wound tube formed with a spirally wound belt-like member wound, in an axis direction of the flexible tube, with clearances between windings; a braided tube that covers the spirally-wound tube, the braided tube being formed with braided plurality of thin wires, a plurality of interstices being distributed on the braided tube; and a sheath that is coated on the braided tube, material of the sheath being fused and coated on the braided tube and then cool-hardened to form the sheath. In such a flexible tube, material of the sheath is caused, when it is fused, to pass through the interstices, which faces the clearances between windings, to form a plurality of protruded portions which protruded inward with respect to the braided tube.
With this structure, since the engagement of the protruded portions and the windings of the spirally-wound tube restricts the relative movement of the spirally-wound tube with respect to the braided tube and the sheath, an appropriate flexibility can be obtained.
Preferably, an outer surface of the spirally-wound tube and an inner surface of the braided tube closely contact such that the material of the sheath has not invaded between the outer surface of the spirally-wound tube and the inner surface of the braided tube.
In one example, the tips of the protruded portions may be located at substantially the same level as the inner surface of the spirally-wound tube.
Alternatively or optionally, the protruded portions may include ones whose tips are located inside the inner surface of the spirally-wound tube.
Further alternatively or optionally, the protruded portions may include ones whose tips are located outside the inner surface of the spirally-wound tube.
Furthermore, the protruded portions may include ones whose protruding amounts are different from each other.
Still optionally, the protruded portions may include a plurality of groups of protruded portions, the tips of the protruded portions of each group are connected at a clearances between the windings of the spirally-wound tube.
In this case, it is preferable that an outer surface of the spirally-wound tube and an inner surface of the braided tube closely contact such that the material of the sheath has not invaded between the outer surface of the spirally-wound tube and the inner surface of the braided tube.
Preferably, the sheath may be formed of fluoride elastomer.
Optionally, the flexible tube further includes an interpolation tube provided inside the spirally-wound tube, tips of the plurality of protruded portions and corresponding portions of the interpolation tube being fused and fixed to each other.
In this case, it is preferable that an outer surface of the spirally-wound tube and an inner surface of the braided tube closely contact such that the material of the sheath has not invaded between the outer surface of the spirally-wound tube and the inner surface of the braided tube.
Further, a fusing point of material of the interpolation tube may be lower than a fusing point of the sheath material so that the material of the interpolation tube is fused by the heat of the sheath material.
Specifically, sheath material may have thermoplastic polyurethane as a main ingredient, and the interpolation tube may be made of material whose main ingredient is one of polyamide, epoxide, polyester or polyurethane.
Optionally, the flexible tube may include a plurality of spirally-wound tubes.
In another example, the plurality of protruded portions may include ones whose tips are formed to be flange portions extending in the axial and/or circumferential direction of the spirally-wound tube.
In this case, it is preferable that the outer surface of the spirally-wound tube and an inner surface of the braided tube closely contact such that the material of the sheath has not invaded between the outer surface of the spirally-wound tube and the inner surface of the braided tube.
Optionally, the flange portions are formed inside the spirally-wound tube, a width of each of the flange portions being longer than a length of a clearance in the axial direction of the spirally-wound tube.
Further optionally, the flange portions may be located within portions between the windings of the spirally-wound tube, and the flange portions may be wider than the interstices formed on the braided tube.
Still optionally, the flexible tube may include a plurality of spirally-wound tubes, and the plurality of protruded portions may include ones which extend in the clearances of all of the plurality of spirally-wound tubes.
In another example, the protruded condition of the plurality of protruded portions are varied in the axial direction of the flexible tube.
In such a case, the flexible tube may have different flexibility in the axial direction.
In particular, the protruded condition may include at least one of a protruded amount, a shape of a protruded portion and a density of the protruded portions.
Specifically, the protruded condition may include at least one of a protruded amount and density of protruded portions, and the protruded condition may be varied by varying braided condition of the braided tube in the axial direction thereof.
Further optionally, the protruded condition of the plurality of protruded portions are varied in the circumferential direction of the flexible tube.
In this case, the flexible tube may have a directivity in the bending direction.
Preferably, the protruded condition includes a protruded amount of the plurality of protruded portions.
In one example, the protruded amount of the plurality of protruded portions may be smaller in one portion along the circumferential direction of the flexible tube than the other portions.
Alternatively, the protruded amount of the plurality of portions may be smaller at two portions which are apart by 180 degrees along the circumferential direction of flexible tube than the other portions.
According to another aspect of the invention, there is provided a method of forming a flexible tube for an endoscope. The flexible tube may include: a spirally-wound tube formed with a spirally wound belt-like member wound, in an axis direction of the flexible tube, with clearances between windings; a braided tube which covers the spirally-wound tube, the braided tube being formed with braided plurality of thin wires, a plurality of interstices being distributed on the braided tube; and a sheath which coats the braided tube, material of the sheath being fused and coated on the braided tube and then cool-hardened to form the sheath.
The method causes the material of the sheath, when fused, to pass through the interstices facing the clearances between windings to form a plurality of protruded portions which protruded inward with respect to the braided tube, the plurality of protruded portions including a plurality of groups of protruded portions, the tips of the protruded portions of each group are connected at a clearances between the windings of the spirally-wound tube. It is preferable that the method includes vulcanizing the sheath after the braided tube is coated by the sheath material.